Strangely, AJDT doesn't show up in the marketplace, even though it is an Eclipse sub-project.
I installed it the old fashioned way.
m2eclipse does appear in the marketplace but, there is not an option to install it (the same for the Spring IDE).
I can't blame Eclipse for this as it's probably an issue with vendor (Sonatype/Spring Source) integration.

Interestingly, when I searched for FindBugs, Sonar also appeared in the search results
(because it's a related plugin?)
I was un aware of this plugin but, I use it in my continuous integration environment so, I decided to install it
and give it a run too.

For the rest, installation is a simple matter of search and click install; pretty awesome.
This is much better than googling for the installs, pasting update site URL's and selecting the correct components
to install.
So, I give Eclipse bonus points for the marketplace and I hope plugin providers get on board with better integration.

Impressive Changes

Once I all of the basics were set-up, I checked my project out of version control.
The first thing I noticed, my projects build much faster.
(side note: This version of Eclipse starts up muuuuch faster)

Old Bugs Rear Their Ugly Heads

In the process of installing plugins, Eclipse hung up while trying to restart.
Basically, while trying to build it's stuck waiting for a server that's offline.
I click the cancel task button, and it took almost 10 minutes to actually cancel.

Maybe one day, the workbench team will get a grasp of multithreading and actually make the cancel kill a thread
instead of hanging the workbench.

The javascript editor that ships with it still finds syntax errors in the jQuery library.
Really? This still isn't fixed?

Another issue, I still see the mysterious "Unknown Error" associated with my project (see below).

Other Changes

There is now support for
virtual Folders.
This will make working with legacy projects with complex build systems much easier.

Type Hierarchy can now be computed in background. Does anybody even use Type Hierarchy?
For me, this is a non-feature but,
I suppose it's useful for those folks that are still extending classes (please stop doing that) willy nilly.
It can be helpful when dealing with legacy code.

Testing

There is a claim for better jUnit4+ support.
However, when I select several packages, right-click, Run As... there is no option to run as "JUnit Test".
It does work if I select a top level source resource, a single package, or a class.
This is one of those minor anoyances that has been with Eclipse for a long time.

Java Stuff

There's a plethora of new options for formatting Java code.
You'll have to just read through them if you install.
None appeared spectacular enough to mention.

There are lots of little improvements around refactoring and many more around the compiler.
Mostly, it's adding warnings where appropriate and just plain acting a bit smarter.

There is now support for package name abbreviations (I swear I remember this in the 2.x versions but, I could be mistaken).
This will be a nice feature, especially in the case where all of your packages start with your company name.

An instance count column has been added to the variable view (for the debug perspective).
At first take, this looks interesting; my first thought, this could help find memory leaks.
However, after messing around, I don't think this offers very much at all.

Conclussion

While my first experience with the Helios wasn't so great, once I got a version
that was usable, things went pretty smooth.

I'm going to try to use Helios exclusively for a while and I'll post updates as I run into
good features and problems.